1. Field of the Invention
The field of the present invention relates to a medical data communication link system and an X-ray CT apparatus (or X-ray diagnosis apparatus) which communicate between a rotating frame that takes radiographic image while rotating and a stationary frame that processes the image data received from the rotating frame. In particular, it relates to communication technology relating to the processing of large amounts of data at a high data rate.
2. Description of the Related Art
As shown in FIG. 1(A), the entire constitution of a conventional X-ray CT apparatus is roughly divided into a rotating frame 200, stationary frame 100 (the combination of the rotating frame 200 and the stationary frame 100 is sometimes referred to as gantry) and a console 300. The rotating frame 200 opens to accommodate an object. The rotating frame 200 is constituted such that it can rotate around the object by a rotation-driving device 211. A rotation control device 212 controls the rotation-driving device 211 upon receipt of an instruction from a control device 350 through a coupler 270. During the rotation of the rotating frame 200, an X-ray control device 222 controls the tube voltage, tube current, etc., of an X-ray tube enclosed in an X-ray source 221 upon receipt of the command from control device 350 through the coupler 270. When an X-ray is radiated onto an object by the X-ray source 221, the X-ray transmitted onto the object is received by an X-ray detector 230 and derived by being converted into electric signals for transmission. The X-ray detector 230 is constituted of a plurality of X-ray detector element arrays. A data collector device 240 collects the electric signals from the X-ray detector element arrays. A transmission unit 250 modulates the electric signals from the data collector 240 into a high frequency carrier signal for high data rate transmission to a transmission medium 260. The carrier signal is transmitted to a reception unit 310 through a receiving medium 110 in the stationary frame 100. Using the transmission medium 260 and the receiving medium 110, the carrier signal is transmitted/received by charge coupling. The reception unit 310 demodulates the transmitted carrier signal, and converts the electric signal obtained by demodulation into digital data. Further, the data is constituted of image data relating to the object by a reconstruction processing device 320 and stored in an image memory 330. An image-processing device 340 produces the required image based on the image data from the image memory 330 upon request from the operating device 361 of a user interface 360, and displays the image on a display device 362.
In such X-ray CT apparatus, communication between the rotating frame 200 and the stationary frame 100 is required. Since communication at the side of the coupler 270 mainly consists of a control command from the control device 350 to the rotation control device 212 and X-ray control device 222, the data volume for communication is comparatively small. Meanwhile, in the X-ray detector 230, many X-ray detector element arrays are provided corresponding to the image pixels in order to obtain a precise image finally. For this reason, there is a large amount of communication in the electric signal transfer between the transmission medium 260 and the receiving medium 110. U.S. Pat. No. 5,530,424 employed a charge-coupling system as the communication technology between the rotating frame 200 and the stationary frame 100, and are incorporated herein by reference.
FIG. 2 typically shows the constitution of communication between the transmission unit 250 and reception unit 310 using the charge-coupling system. The electric signal output from the transmission unit 250 is branched into two signals that are equally halved at a branch 250a. The branch 250a consists of an amplifier and a resistor. The branched electric signals are output to a transmission medium 260a and transmission medium 260b, and individually terminated at a terminal 250b. The transmission medium 260a and transmission medium 260b are located in a line around the circumference of the rotating frame 200. The transmission medium 260a and transmission medium 260b extend around the circumference respectively. During rotation, transmission medium 260a and transmission medium 260b are charge-coupled with the receiving medium 110 mounted to the stationary frame 100, and the electric signal is transferred to the receiving medium 110. The receiving medium 110 further transfers the electric signal to the reception unit 310.
In the constitution of FIG. 2, as the length of the transmission line of the route of transmission unit 250—branch 250a—transmission medium 260a—terminal 250b and the length of the transmission line of the route of transmission unit 250—branch 250a—transmission medium 260b—terminal 250b are arranged in the same length, even if the branch 250a or the terminal 250b is hung over the receiving medium 110, the receiving medium 110 can obtain a signal with the same phase (the same time delay) from both the transmission medium 260a and transmission medium 260b due to rotation of the rotating frame 200, thus obtaining a continuous signal without mixing the signals.
Recently, more accurate images are required in a shorter time for medical examinations. Under the circumstances, as shown in FIG. 1(B) for example, with an X-ray detector, the X-ray detector element array has been composed of a plurality of lines and columns with an increasing communication volume in a massive amount. In such a situation, the conventional technology conducts communication by raising the communication frequency (or transfer speed) by several GHz (or GBps). However, because communication occurs through one channel, the above requirements cannot be satisfied.
As one of the methods to respond to such requirements as shown in FIG. 3, the communication system with one channel shown in FIG. 1 may be changed to that of the rotating frame of N layered components shown in FIG. 2, resulting in communication capacity of a plurality of N channels. As clearly shown in FIG. 3, however, this method increases the width of the system, thus having a disadvantage of increasing the space required for installation of the X-ray CT apparatus. Meanwhile, in order to increase the communication capacity, increasing the transmission speed may be considered. However, increasing the transmission speed creates many problems to be solved, such as difficulty in obtaining the same phase (propagation delay) as explained above, and therefore is judged to be impractical.